Plants Provide NEW DRUG LEADS
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Medicinal plants have been used for therapeutic purposes since the beginning of civilization. Following a recent period in Western medicine when plant medicines were shunned, there has been a resurgence of interest in plant compounds with beneficial pharmacological properties. The development of these agents is a long and expensive undertaking. This paper outlines the necessary steps to accomplish this task.
According to the author, development of new drugs can cost as much as $360 million and take a minimum of 10 years. Tens of thousands of compounds are tested before one possible drug is found, and large volumes of plant materials are necessary to obtain very small amounts of active compounds. The effort is multidisciplinary, requiring botanists, chemists, pharmacologists, toxicologists, and agronomists. Medically active plants can be used as teas or extracts, or they can be purified to active compounds. If the medicine is derived solely from a plant and retains the plant's chemical complexity, it is considered a phytopharmaceutical preparation or herbal medicine. If it is an isolated compound and prepared according to specific legal and technical procedures, it is considered a drug.
Plants chosen for drug development are most commonly selected based on their use in folk and traditional medicine. The study of these uses is called ethnobotany. Plants can also be selected based on chemical constituents known to their families or genera. This has been especially productive in toxic plants. Randomized searching for plants with specific pharmacological activities is another approach.
Existing scientific literature can also be used to identify known compounds with promise. Use of natural resources for drug development must be accompanied by sustainable practices and respect for the environment and cultures where they originate. The most commonly sought-after treatments are antibiotics, anti-tumor drugs, contraceptives, anti-inflammatories, kidney protectors and drugs for psychiatric and tropical diseases.
Once chosen, a plant must be correctly identified and preserved. It is then analyzed for active compounds which are isolated using appropriately selected laboratory methods. Additional work is done to identify the chemical structure which will allow total or partial synthesis and alteration of the structure to improve efficacy (or reduce toxicity).
Extensive efficacy and toxicity studies follow. Crude preparations of the whole plant can be developed as herbal remedies. Efficacy and safety studies are required in this case as well, but are less extensive, and, according to the author, historical use can be taken as proof of efficacy. (However, in the regulatory systems of some Western nations, historical use is not considered an adequate criterion for safety and efficacy.) Whole plant preparations are appropriate when a combination of compounds are active. Some of the challenges of developing crude preparations are low concentrations of active compounds, poor bioavailability, and solubility.
Because plant medicines are freely marketed in many parts of the world, toxic accidents sometimes result. These accidents can be due to mistaken identification of plants, inherent toxicity, and misuse. Some plants interfere with pharmaceutical drugs, including those containing coumarins, tyramine, estrogenic or photosensitive compounds, or those which cause allergic reactions.
A large percentage of the plants on Earth are found in Brazil; however, the pharmaceutical industry there is only in developmental stages. Herbal medicine companies are usually small, and research is limited to a small number of university staff. Quality standards remain minimal. The country is putting into place guidelines based on the World Health Organization, the European Scientific Cooperative on Phytotherapy, and the German Commission E, and is forging partnerships between the academic and pharmaceutical sectors. There is still much room for growth in the areas of research, publication of findings, and active collaborations. Finally, legislation is being developed to preserve the natural diversity of the country and encourage sustainable development of its resources.
-Risa N. Schulman, Ph.D.
Rates, SMK. 2001. Plants as source of drugs. Toxicon, 39: 603-613 The American Botanical Council (ABC) is the world's leading non-profit education organization disseminating science-based information promoting the safe and effective use of herbal medicine.
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